1. Technical Field
The present invention relates to circulating liquid systems having a tank or tub of liquid and a recirculating pump, with one or more suction ports in the tank, and using one or more submerged return ports from the pump. The piping between tank and pump may also contain a heater, and the return line may have provision for an injector nozzle to entrain air or other fluid. One application particularly envisioned is the commonly used hot tub, or spa, for bathing. A number of accidents have occurred in hot tubs, where the powerful suction which is associated with the high flow requirements of these tubs has held persons underwater. There is thus a need for a system which avoids the capture of objects within the tub by the suction port.
2. Background of the Prior Art
Prior art liquid circulation systems of the type considered here have employed multiple suction ports, distributed about the tank, and connected in parallel to the pump. Use of multiple suction ports promoted better mixing of liquid, by drawing from all ports of the tank. More importantly to the hot-tub application, the full power of the pump is divided among the multiple suction ports, thereby reducing the chance that a body may be drawn to a suction port and held tightly. However, there have been continuing instances of persons drowning because hair or loose clothing was drawn into one of multiple suction ports and held too tightly to be removed by the individual. Hair and clothing items are particularly vulnerable to such occurrences because they do not completely block the flow and are thus subjected to high dynamic pressures associated with the high flow velocities used in hot tubs, even with multiple ports. Furthermore, the use of multiple suction ports is undesirable because of the proliferation of openings through the tank wall. Each such opening is a potential leak, and contributes to weakening of the wall. In principle, multiple suction ports could provide sufficient distributed area to assure that suction flow at the tank wall avoids any possibility of accident, but practical applications do not usually achieve the desired objective. The same considerations apply to industrial mixing systems which are unreliable with the external pump system considered here when the tank contains floating solid objects.